1. Field of the Invention
This invention relates to the in-situ retorting of carbonaceous deposits, and more particularly to apparatus for control of the flow of products produced during the in-situ retorting of such deposits.
2. Description of the Prior Art
Very large potential sources of fluid fuels exist in subsurface deposits of carbonaceous materials that are either solid materials or so highly viscous that they cannot be made to flow through the subsurface formation to a production well. Among such deposits are oil shale, tar sands and coal. One method of producing fluid fuels from such deposits is to ignite the deposits and continue after ignition to inject an oxygen-containing gas, usually air, into the deposits to burn some of the carbonaceous material. If an in-situ combustion process is utilized for production of shale oil from oil shale, the shale is heated to a temperature at which kerogen in the oil shale is converted to shale oil which is then made to flow to facilities for lifting the shale oil to the surface. In-situ combustion of tar sands raises the temperature of the sands to a temperature at which the oil has a viscosity sufficiently low to allow it to flow to production facilities. Cracking of the oil further reduces its viscosity, and the pressure of the injected air drives the oil toward the production well. The maintenance of combustion in coal deposits is designed principally to convert carbon in the coal to gaseous materials, principally carbon monoxide, which can be used as a fuel.
Shale deposits, coal deposits, and some of the tar sands have a permeability that is so low that even if the carbonaceous material is converted to fluids, flow to a production facility at a rate high enough to continue the combustion cannot be maintained. One method that has been proposed to overcome the low permeability of the carbonaceous deposit is to form rubblized in-situ retorts of the carbonaceous deposit. Several suitable processes for the formation of rubblized in-situ retorts and the production of fluid fuels therefrom are described in U.S. Pat. No. 1,919,636 of S. N. Karrick, U.S. Pat. No. 3,001,776 of H. K. Van Poollen and U.S. Pat. No. 2,481,051 of L. C. Uren. Rubblized retorts can be used for in-situ combustion processes and also for other retorting schemes such as injection of hot flue gases or steam into the retort.
In the systematic exploitation of a subsurface deposit of a material such as oil shale, retorts are constructed in rows and retorting of rubblized shale is conducted in one or more of the retorts in the row while construction of other rubblized retorts in the row is proceeding. The gaseous products produced in the in-situ combustion operations are highly toxic. It is important to isolate retorts under construction from retorts in which combustion is in progress. In a preferred method of preventing flow of combustion products from a retort in which combustion is in progress through fissures or fractures in the carbonaceous deposit to a retort in which men are working, a rubblized retort between the combustion and mining retorts is maintained under air pressure higher than the pressure in both the retorts in which combustion is in progress and the retorts in which men are working.